Yongsuk Seo

Hemodynamic and thermoregulatory responses to lower body water immersion.

INTRODUCTION Lower body water immersion (LBWI) is experienced in the marine industry but the physiological responses to LBWI are unclear. The purpose of the current experiment was to test the effects of water temperature and immersion duration on rectal temperature, heart rate, stroke volume, blood pressure, metabolic rate, and thermal sensation in healthy subjects. METHODS Nine young men underwent two 60-min trials of seated LBWI to the iliac crest in a counterbalanced fashion. On one occasion, the water was 35 degrees C (LBWI-Neutral) and on the other it was 13 degrees C (LBWI-Cold); the upper body remained thermoneutral and dry throughout. RESULTS As expected, exposure to cold water reduced mean skin temperature and individuals reported cold thermal sensation. Mean arterial pressure was significantly higher at 60 min of LBWI-Cold (86 +/- 7 mmHg) compared to LBWI-Neutral (76 +/- 5 mmHg) while heart rate tended to be lower. The change in rectal temperature from baseline to 30 min of LBWI-Cold (delta = -0.01 +/- 0.21degrees C) was significantly smaller than the change in T(re) from 30 to 60 min of LBWI-Cold (delta = -0.46 +/- 0.16 degrees C). Despite this accelerated drop in core temperature during minutes 30-60, metabolic rate did not increase significantly. CONCLUSION LBWI-Cold reduces core temperature and increases arterial blood pressure via an increase in total peripheral resistance. This experimental model may help scientists better understand the body during cold stress. Further, people who are occupationally exposed to cold water (when the torso, hands, and arms remain thermoneutral) may be at increased risk for hypothermia.

Effect of Caffeine Intake on Finger Cold-Induced Vasodilation

OBJECTIVE The purpose of the study was to investigate the effect of caffeine intake on finger cold-induced vasodilation (CIVD). METHODS Ten healthy men underwent 6 experimental trials characterized by control (NCAFF) or caffeine intake (CAFF) via chewing gum (300 mg of caffeine) while resting on a chair or performing submaximal (70% maximal oxygen consumption) or maximal (100% maximal oxygen consumption) treadmill exercise (Bruce protocol) followed by immersion of the middle finger in a water bath (5°C) for 20 minutes. Finger temperature (Tf ) and time parameters of the first CIVD cycle and post-test norepinephrine were measured. RESULTS Exercise duration for submaximal and maximal exercise was 8.9 ± 0.9 and 12.4 ± 0.8 minutes, respectively. CAFF had no effect on Tf, but exercise increased minimal Tf in NCAFF (9.08 ± 1.27°C, 13.02 ± 2.13°C, and 13.25 ± 1.63°C in rest, submaximal, and maximal exercise, respectively) and CAFF (8.76 ± 1.39°C, 12.50 ± 1.91°C, and 12.79 ± 1.20°C). Maximal Tf was significantly higher in NCAFF (15.98 ± 1.04°C, 16.18 ± 1.56°C, and 15.14 ± 1.52°C) than in CAFF (13.56 ± 1.19°C, 15.52 ± 1.31°C, and 14.39 ± 1.43°C), resulting in a significant difference between minimal and maximal Tf in rest (NCAFF, 6.89 ± 1.56°C and CAFF, 4.79 ± 1.23°C), but not in exercise conditions. CAFF had no effect on CIVD time responses, but exercise significantly shortened CIVD onset and peak time compared with rest in both NCAFF and CAFF. Norepinephrine concentration was significantly greater in CAFF (290.6 ± 113.0 pg/mL, 278.1 ± 91.4 pg/mL, and 399.8 ± 125.5 pg/mL) than NCAFF (105.6 ± 29.5 pg/mL, 199.6 ± 89.6 pg/mL, and 361.5 ± 171.3 pg/mL). CONCLUSIONS Caffeine intake before finger immersion in cold water does not result in a thermogenic effect and adversely affects CIVD responses, whereas exercise modifies CIVD temperature and time responses.

The Influence of Exercise on Cognitive Performance in Normobaric Hypoxia

Although previous reports indicate that exercise improves cognitive function in normoxia, the influence of exercise on cognitive function in hypoxia is unknown. The purpose of this study was to determine if the impaired cognitive function in hypoxia can be restored by low to moderate intensity exercise. Sixteen young healthy men completed the ANAM versions of the Go/No-Go task (GNT) and Running Memory Continuous Performance Task (RMCPT) in normoxia to serve as baseline (B-Norm) (21% O2). Following 60 minutes of exposure to normobaric hypoxia (B-Hypo) (12.5% O2), these tests were repeated at rest and during cycling exercise at 40% and 60% of adjusted Vo2max. At B-Hypo, the % correct (p≤0.001) and throughput score (p≤0.001) in RMCPT were significantly impaired compared to B-Norm. During exercise at 40% (p=0.023) and 60% (p=0.006) of adjusted Vo2max, the throughput score in RMCPT improved compared to B-Hypo, and there was no significant difference in throughput score between the two exercise intensities. Mean reaction time also improved at both exercise intensities compared to B-Hypo (p≤0.028). Both peripheral oxygen saturation (Spo2) and regional cerebral oxygen saturation (rSo2) significantly decreased during B-Hypo (p≤0.001) and further decreased at 40% (p≤0.05) and 60% (p≤0.039) exercise. There was no significant difference in Spo2 or rSo2 between two exercise intensities. These data indicate that low to moderate exercise (i.e., 40%-60% adjusted Vo2max) may attenuate the risk of impaired cognitive function that occurs in hypoxic conditions.

Cognitive function during lower body water immersion and post-immersion afterdrop.

INTRODUCTION The physiological effects of immersion hypothermia and afterdrop are well-characterized, but the psychological effects are less clear. The purpose of this study was to quantify changes in cognitive function during and after lower body water immersion. METHODS On separate mornings, nine young healthy men participated in both neutral (35 +/- 1 degree C) and cold (13 +/- 1 degree C) water immersion. Subjects rested in neutral air for 30 min followed by 60 min water immersion to the iliac crest and 15 min of recovery in neutral air. Rectal temperature and mean skin temperature were continuously monitored. Metabolic rate, the Stroop Color Word Test (SCWT), and the Profile of Mood State (POMS) were quantified at predetermined intervals. RESULTS During immersion in cold water, rectal temperature was reduced, but SCWT and POMS scores were unchanged relative to baseline. Despite the reduced rectal temperature, little to no shivering was observed during immersion and metabolic rate did not change. During recovery from cold immersion, rectal temperature was further reduced by approximately 0.5 degree C, shivering was noted, and metabolic rate increased. Coincident with this acute afterdrop, SCWT Color-Word performance (delta = -4 +/- 8 vs. 7 +/- 6 correct responses) and Interference score (delta = -2 +/- 7 vs. 4 +/- 8) was impaired relative to recovery from neutral immersion (i.e., when core temperature and metabolic rate did not change). CONCLUSION These results suggest that recovery from lower body cold water immersion elicits the afterdrop phenomenon and shivering, which together impair selective attention as measured by the SCWT.

Do glucose containing beverages play a role in thermoregulation, thermal sensation, and mood state?

IntroductionDehydration limits the appropriate delivery of oxygen and substrates to the working muscle. Further, the brain’s ability to function may also be compromised whereby thermal sensation and mood state may be altered.PurposeThe purpose of the present investigation was to compare the thermoregulatory, perceptual, and negative mood state profile in glucose (GLU) vs. non-glucose beverage (NON-GLU) condition.MethodsTen healthy men volunteered and were counterbalanced either a GLU or NON-GLU containing beverage on separate mornings. In each condition, they were exposed to 37°C, 50% relative humidity (RH) for baseline, exercise, rehydration, and recovery periods. The exercise period elicited the desired level of dehydration (mean of 2.6 ± 0.3% body weight losses). Upon completion of the protracted exercise, participants were administered either a GLU or NON-GLU containing electrolyte based sports drink ad libitum for 30 min, followed by a recovery period of 15 min in 37°C, 50% RH. Rectal (Tre) and mean skin temperatures (Tsk) were continuously monitored. Gagge (TS) and heated thermal sensation (HTS), profile of mood state (POMS) were measure at the end of each period.ResultsDuring recovery after rehydration, Tre was not significantly different between conditions (GLU vs. NON-GLU) (37.4 ± 0.8 vs. 37.0 ± 1.2°C); Tsk was also not affected by rehydration in both conditions (36.0 ± 0.5 vs. 36.0 ± 0.6°C) and, TS and HTS did not differ between conditions (0.9 ± 1.3 vs.1.3 ± 0.7) and (1.0 ± 0.8 vs.0.8 ± 0.3). Total mood disturbance (TMD) score for the POMS was utilized for overall negative mood state and demonstrated a main effect for time (p < 0.05). TMD during recovery was decreased compared to before hydration in both conditions.ConclusionThe non-glucose containing beverage maintained plasma volume and was effective at maintaining body temperature homeostasis in a similar fashion compared to the glucose containing beverage. Furthermore, negative mood state was not different between the two conditions. The non-glucose beverages can serve a valuable role in the exercise environment depending upon the sport, the ambient temperature, the individual, duration of the exercise, the age and training states of the individual.

Pilot physiology, cognition and flight performance during flight simulation exposed to a 3810-m hypoxic condition

Background. Hypoxia is a physiological state defined as a reduction in the distribution of oxygen to the tissues of the body. It has been considered a major factor in aviation safety worldwide because of its potential for pilot disorientation. Pilots are able to operate aircrafts up to 3810 m without the use of supplemental oxygen and may exhibit symptoms associated with hypoxia. Objective. To determine the effects of 3810 m on physiology, cognition and performance in pilots during a flight simulation. Methods. Ten healthy male pilots engaged in a counterbalanced experimental protocol comparing a 0-m normoxic condition (NORM) with a 3810-m hypoxic condition (HYP) on pilot physiology, cognition and flight performance. Results. Repeated-measures analysis of variance demonstrated a significant (p ≤ 0.05) time by condition interaction for physiological and cognitive alterations during HYP. A paired-samples t test demonstrated no differences in pilot performance (p ≥ 0.05) between conditions. Conclusion. Pilots exhibited physiological and cognitive impairments; however, pilot performance was not affected by HYP.

Cerebral Hemodynamics and Executive Function During Exercise and Recovery in Normobaric Hypoxia

BACKGROUND Hypoxia and exercise each exhibit opposing effects on executive function, and the mechanisms for this are not entirely clear. This study examined the influence of cerebral oxygenation and perfusion on executive function during exercise and recovery in normobaric hypoxia (NH) and normoxia (N). METHODS There were 18 subjects who completed cycling trials in NH (12.5% FIo2) and N (20.93% FIo2). Right prefrontal cortex (PFC) oxyhemoglobin (O2Hb) and middle cerebral artery blood velocity (MCAbv) were collected during executive function challenges [mathematical processing and running memory continuous performance task (RMCPT)] at baseline, following 30 min of acclimation, during 20 min of cycling (60% Vo2max), and at 1, 15, 30, and 45 min following exercise. RESULTS Results indicated effects of time for Math, RMCPT, and O2Hb; but not for MCAbv. Results also indicated effects of condition for O2Hb. Math scores were improved by 8.0% during exercise and remained elevated at 30 min of recovery (12.5%), RMCPT scores significantly improved at all time points (7.5-11.9%), and O2Hb increased by 662.2% and 440.9% during exercise in N and NH, respectively, and remained elevated through 15 min of recovery in both conditions. DISCUSSION These results support the influence of PFC oxygenation and perfusion on executive function during exercise and recovery in N and NH.Stavres J, Gerhart HD, Kim J-H, Glickman EL, Seo Y. Cerebral hemodynamics and executive function during exercise and recovery in normobaric hypoxia. Aerosp Med Hum Perform 2017; 88(10):911-917.

Normobaric Hypoxia and Submaximal Exercise Effects on Running Memory and Mood State in Women

BACKGROUND An acute bout of exercise can improve cognitive function in normoxic and hypoxic conditions. However, limited research supports the improvement of cognitive function and mood state in women. The purpose of this study was to examine the effects of hypoxia and exercise on working memory and mood state in women. METHODS There were 15 healthy women (age = 22 ± 2 yr) who completed the Automated Neuropsychological Assessment Metrics-4th Edition (ANAM), including the Running Memory Continuous Performance Task (RMCPT) and Total Mood Disturbance (TMD) in normoxia (21% O2), at rest in normoxia and hypoxia (12.5% O2), and during cycling exercise at 60% and 40% Vo2max in hypoxia. RESULTS RMCPT was not significantly impaired at 30 (100.3 ± 17.2) and 60 (96.6 ± 17.3) min rest in hypoxia compared to baseline in normoxia (97.0 ± 17.0). However, RMCPT was significantly improved during exercise (106.7 ± 20.8) at 60% Vo2max compared to 60 min rest in hypoxia. Following 30 (-89.4 ± 48.3) and 60 min of exposure to hypoxia (-79.8 ± 55.9) at rest, TMD was impaired compared with baseline (-107.1 ± 46.2). TMD was significantly improved during exercise (-108.5 ± 42.7) at 40% Vo2max compared with 30 min rest in hypoxia. Also, RMCPT was significantly improved during exercise (104.0 ± 19.1) at 60% Vo2max compared to 60 min rest in hypoxia (96.6 ± 17.3). DISCUSSION Hypoxia and an acute bout of exercise partially influence RMCPT and TMD. Furthermore, a moderate-intensity bout of exercise (60%) may be a more potent stimulant for improving cognitive function than low-intensity (40%) exercise. The present data should be considered by aeromedical personnel performing cognitive tasks in hypoxia.Seo Y, Gerhart HD, Stavres J, Fennell C, Draper S, Glickman EL. Normobaric hypoxia and submaximal exercise effects on running memory and mood state in women. Aerosp Med Hum Perform. 2017; 88(7):627-632.

Low intensity exercise does not impact cognitive function during exposure to normobaric hypoxia

Exposure to hypoxia is associated with cognitive impairment, mediated by cerebral deoxygenation. This can be problematic for individuals who perform mental tasks at high altitude. Eight healthy men completed two experimental trials consisting of 5h of exposure to normobaric hypoxia (12.5% O2). In one of the experimental trials (Hypoxia) subjects remained resting in a seated position the entire 5h; in the other experimental trial (Hypoxia and Exercise) subjects rested 2h, cycled for 1h at constant wattage (workload equivalent to 50% of altitude adjusted VO2max), then rested the last 2h. Cerebral oxygenation was measured continuously via near-infrared spectroscopy and cognitive performance was assessed by Trail Making Test A and B. Cerebral oxygenation and cognitive performance both were impaired during exposure to hypoxia. In the Hypoxia and Exercise trial, subjects experienced further declinations in cerebral oxygenation without concomitant decreases in cognitive function. These data demonstrate that cognitive function declines during exposure to normobaric hypoxia and this decline is not exacerbated by low intensity exercise.

Exercise Improves Mood State in Normobaric Hypoxia.

BACKGROUND The purpose of this study was to quantify the efficacy of using exercise to alleviate the impairments in mood state associated with hypoxic exposure. METHODS Nineteen young, healthy men completed Automated Neuropsychological Assessment Metrics-4(th) Edition (ANAM4) versions of the mood state test before hypoxia exposure, after 60 min of hypoxia exposure (12.5% O(2)), and during and after two intensities of cycling exercise (40% and 60% adjusted Vo(2max)) under the same hypoxic conditions. Peripheral oxygen saturation (Spo(2)) and regional cerebral oxygen saturation (rSo(2)) were continuously monitored. RESULTS At rest in hypoxia, Total Mood Disturbance (TMD) was significantly increased compared to baseline in both the 40% and 60% groups. TMD was significantly decreased during exercise compared to rest in hypoxia. TMD was also significantly decreased during recovery compared to rest in hypoxia. Spo(2) significantly decreased at 60 min rest in hypoxia, during exercise, and recovery compared to baseline. Regional cerebral oxygen saturation was also reduced at 60 min rest in hypoxia, during exercise, and recovery compared to baseline. DISCUSSION The current study demonstrated that exercise at 40% and 60% of adjusted Vo(2max) attenuated the adverse effects of hypoxia on mood. These findings may have significant applied value, as negative mood states are known to impair performance in hypoxia. Further studies are needed to replicate the current finding and to clarify the possible mechanisms associated with the potential benefits of exercise on mood state in normobaric hypoxia.